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It was easy to turn the laser on but unfortunally the red diode needs less current than the blue and when we turn it on it auto-destroyed. It happend three times till we deducted the problem, so we killed three pickups during this testing. Now that we know the problem we are limiting the current of the red laser diode and.....

The first idea was to focus the laser on four reflecting focus points we glued under the glass. The robot automatically moves the toolhead to those focus points and take four focus measures. Then it uses them to extrapolate the data to the rest of the PCB so it can accurately focus the laser while rastering the PCB picture. But we had some problems with the glass thickness. We were using an inadequate 2mm glass and we had to change to 1.5mm glass which works better. But even with the new glass we were not satisfied because the focus points were too far from the PCB corners so the measures were not accurate.

If we wanted to improve the focus accuracy we had to focus on the PCB corners. This is not a problem because the PCB is reflective enough to focus directly on it but as always happens appeared two secondary effects.

First we “paint” four blots on the PCB dry-film because the UV laser sensitizes it on the places it focuses. Second we have to focus through the glass and the solar film. Remember that we use the solar film to filter the UV rays and protect the PCB from the “halo” effect produced by the pickup lens. The filter is good while we printing but diminish performance when we focus. So we were again in a dead-end alley.

I think we found a solution: the red laser.

The PHR-803T is fantastic. It has three laser diodes: one in the infrared band for reading CDs, one on the red band for DVDs and one on the near UV band for HD-DVD/Blu-ray. When we hacked the pickup we didn’t paid too much effort on the red lasers because we were focus on sensitize the dry-film with UV light but I think we are going to use the red one now.

Last days we have been working on the 3D Printing Toolhead. We did several printing tests with good results and we found the speed limits of the machine which are aprox. 3500 mm/min (when 3D printing)

Also we improved the server side software. We added functionality to control the 3D printing extruder and the hot-end temperature.

We also developed a firmware algorithm to test how efficient is the auto-levelling algorithm. We had some doubts about if really the algorithm worked fine but they were unfounded because it does and the platform is always levelled with a precision of less than 0.01 mm.

Some days ago we described how we designed the bed to fulfil all the requirements. In this way we built all the components of the bed in order to test if the complete system works with the different tools and finally it looks like this:

We are using a 15 wire cable and a DB15 connector for carry all the signal and power lines that any tool might need. The idea is that every toolhead will use that DB15 connector with a standard pinout. In this way, It will be easy toolhead substitution.

The following is a list of preliminary specifications for the new robot:

Working area

70x80x80mm (X,Y,Z). We reduced it considerably to an Arduino Shield size. In fact sometimes we call the robot “The Arduino Shield Maker”. We reduced it because we preferred to do something small but precise. Rarely all of we create big circuit boards but if you need it you can always split the circuit in two or more modules. Reducing the working area has some advantages: the robot is cheaper, more precise, robust, smaller and more manageable.

Motion

MKII is powered by three Nema 17 motors and Acme screws. We substituted the timing belts we used in MKI in order to eliminate vibration and resonances. It was mainly the solution and now the laser draws on the PCB with a stable beam without any mechanic disturbance.

Speed

We can go as fast as 1200-1500mm/min. We think it’s enough for our purposes. The Acme screw pitch set the limits. The robot can go faster upgrading the screws to ones with more pitch but at a price.